std::malloc
<cstdlib>
Allocates size bytes of uninitialized storage.
If allocation succeeds, returns a pointer to the lowest (first) byte in the allocated memory block that is suitably aligned for any scalar type (at least as strictly as std::max_align_t ) (implicitly creating objects in the destination area).
If size is zero, the behavior is implementation defined (null pointer may be returned, or some non-null pointer may be returned that may not be used to access storage, but has to be passed to std::free ).
The following functions are required to be thread-safe:
- The library versions of operator new and operator delete
- User replacement versions of global operator new and operator delete
- std::calloc , std::malloc, std::realloc , std::aligned_alloc (since C++17), std::free
Calls to these functions that allocate or deallocate a particular unit of storage occur in a single total order, and each such deallocation call happens-before the next allocation (if any) in this order.
(since C++11)Contents
[edit] Parameters
[edit] Return value
On success, returns the pointer to the beginning of newly allocated memory. To avoid a memory leak, the returned pointer must be deallocated with std::free() or std::realloc() .
On failure, returns a null pointer.
[edit] Notes
This function does not call constructors or initialize memory in any way. There are no ready-to-use smart pointers that could guarantee that the matching deallocation function is called. The preferred method of memory allocation in C++ is using RAII-ready functions std::make_unique , std::make_shared , container constructors, etc, and, in low-level library code, new-expression.
For loading a large file, file mapping via OS-specific functions, e.g. mmap on POSIX or CreateFileMapping(A/W) along with MapViewOfFile on Windows, is preferable to allocating a buffer for file reading.
[edit] Example
#include <cstdlib> #include <iostream> #include <memory> #include <string> int main() { constexpr std::size_t size = 4; if (auto ptr = reinterpret_cast<std::string *>(std::malloc(size * sizeof(std::string )))) { try { for (std::size_t i = 0; i < size; ++i) std::construct_at (ptr + i, 5, 'a' + i); for (std::size_t i = 0; i < size; ++i) std::cout << "ptr[" << i << "] == " << ptr[i] << '\n'; std::destroy_n (ptr, size); } catch (...) {} std::free (ptr); } }
Output:
p[0] == aaaaa p[1] == bbbbb p[2] == ccccc p[3] == ddddd